Present telecommunication system technology includes a wide variety of wireless networking systems associated with both voice and data communications. An overview of several of these wireless networking systems is presented by Amitava Dutta-Roy, Communications Networks for Homes, IEEE Spectrum, pg. 26, December 1999. Therein, Dutta-Roy discusses several communication protocols in the 2.4 GHz band, including IEEE 802.11 direct-sequence spread spectrum (DSSS) and frequency-hopping (FHSS) protocols. A disadvantage of these protocols is the high overhead associated with their implementation. A less complex wireless protocol known as Shared Wireless Access Protocol (SWAP) also operates in the 2.4 GHz band. This protocol has been developed by the HomeRF Working Group and is supported by North American communications companies. The SWAP protocol uses frequency-hopping spread spectrum technology to produce a data rate of 1 Mb/sec. Another less complex protocol is named Bluetooth after a 10th century Scandinavian king who united several Danish kingdoms. This protocol also operates in the 2.4 GHz band and advantageously offers short-range wireless communication between Bluetooth devices without the need for a central network.
The Bluetooth protocol provides a 1 Mb/sec data rate with low energy consumption for battery powered devices operating in the 2.4 GHz ISM (industrial, scientific, medical) band. The current Bluetooth protocol provides a 10-meter range and an asymmetric data transfer rate of 721 kb/sec. The protocol supports a maximum of three voice channels for synchronous, CVSD-encoded transmission at 64 kb/sec. The Bluetooth protocol treats all radios as peer units except for a unique 48-bit address. At the start of any connection, the initiating unit is a temporary master. This temporary assignment, however, may change after initial communications are established. Each master may have active connections of up to seven slaves. Such a connection between a master and one or more slaves forms a “piconet.” Link management allows communication between piconets, thereby forming “scatternets.” Typical Bluetooth master devices include cordless phone base stations, local area network (LAN) access points, laptop computers, or bridges to other networks. Bluetooth slave devices may include cordless handsets, cell phones, headsets, personal digital assistants, digital cameras, or computer peripherals such as printers, scanners, fax machines and other devices.
The Bluetooth protocol uses time-division duplex (TDD) to support bi-directional communication. Spread-spectrum technology or frequency diversity with frequency hopping permits operation in noisy environments and permits multiple piconets to exist in close proximity. The frequency hopping scheme permits up to 1600 hops per second over 79 1-MHZ channels or the entire ISM spectrum. Various error correcting schemes permit data packet protection by ⅓ and ⅔ rate forward error correction. Further, Bluetooth uses retransmission of packets for guaranteed reliability. These schemes help correct data errors, but at the expense of throughput.
The Bluetooth protocol is specified in detail in Specification of the Bluetooth System, Version 1.0A, Jul. 26, 1999, which is incorporated herein by reference.
Copending U.S. Ser. No. 09/489,668 filed on Jan. 24, 2000 (incorporated herein by reference) presents a Bluetooth system including a multi-antenna master which is operable to calculate weighting coefficients for its respective antennas based on channel measurements made on transmissions received by the respective antennas. These weighting coefficients are used by the master when transmitting via its plural antennas. In order to enhance the effectiveness of the calculated weighting coefficients, the master deviates from its normal frequency hopping pattern such that the transmit frequency from the master to a given slave is always the same as the transmit frequency that the slave last used to transmit to the master, which latter frequency is specified by the slave's normal frequency hopping pattern. In this manner, the master has an opportunity to measure the channel between the master and the slave at the same frequency that the master will soon use for its next transmission to that slave. This channel measurement opportunity soon before the next master transmission to the slave, and on the same frequency that the master will use in that transmission, increases the effectiveness of the calculated weighting coefficients that will be used in the transmission to the slave.
However, the fact that the master does deviate from its normal frequency hopping pattern in the above-described operation presents some disadvantages. For example, if the master wishes to address an ACL (Asynchronous Connection-Less) slave while using an SCO (Synchronous Connection-Oriented) link, the master would use the frequency dictated by its normal frequency hopping pattern, but the SCO slave would be listening on the frequency that it last used to transmit to the master. Accordingly, the SCO slave will not receive the expected packet, and will therefore respond with a negative acknowledgment (NAK in Bluetooth) indicating that the expected packet was not received. This negative acknowledgment will disadvantageously collide with the ACL slave's response to the master's transmission. A similar problem could arise if the master attempts to send an ACL broadcast packet on an SCO link.
It is therefore desirable to avoid the above-described collision problem while still providing the master with the aforementioned channel measurement opportunity.
The present invention avoids the above-described collision problem for SCO links by appropriately modifying the slave's frequency hopping pattern such that each slave-to-master transmission is on the same frequency that the master's normal frequency hopping pattern specifies for the master's next transmission (or for one of the master's next several transmissions) to that slave. In this manner, the aforementioned collision problem is avoided, because the master's normal frequency hopping pattern advantageously remains unchanged. Furthermore, the aforementioned channel measurement opportunity is retained, because the master still advantageously receives the slave's transmission on a frequency that the master will soon use for transmission to the slave.